Hydrocarbons are a major source of energy for much of the world's energy needs. Recent cost increases in hydrocarbon-based fuels, induced in part by increased demand for hydrocarbons from developing countries and concerns of supply shortages due to the increased demand, has generated increased interest in finding alternative sources of energy for the world's needs. In researching alternative energy sources, focus has been directed to those energy sources meeting at least the criteria of being inexpensive, renewable, and plentiful.
One such alternative energy source capable of meeting the aforementioned criteria has been developed from biological waste products. Biological waste products are a desirable energy source due to the prevalence of such products, and the accompanying need to dispose of these products in an environmentally prudent manner. Such biological waste products are generally referred to as biomass and may include agricultural and other cellulosic waste materials. Nonlimiting examples of biomass may include forest residues, agricultural residues, nuts, nut shells, wood chips, olive and grape mash, and urban biomass, such as municipal solid waste.
Biomass may be converted into a useful gas mixture through a process of gasification. Generally, gasification is a process that converts at least a portion of the biomass material into a useful gas mixture, commonly referred to as synthesis gas (or syngas), through the reaction of the biomass material at high temperatures (>700° C.) with a controlled amount of oxygen and/or steam. Synthesis gas is combustible and may be utilized, for example, as a fuel gas in gas and steam boiler plants, as an intermediate in generating synthesis natural gas, or for the production of other chemicals, such as methanol.
The gasification process may be carried out at least in part in a gasification unit, commonly referred to as a gasifier. The gasifier may be, for example, a counter-current fixed bed gasifier, a co-current fixed bed gasifier, a fluidized bed gasifier, an entrained flow gasifier, or a plasma gasifier. The type of gasifier utilized may be based in part on particular technological and/or commercial needs or factors. For instance, the fluidized bed gasifier may be very useful for feed fuels forming highly corrosive ash due to the propensity of such ash to damage the walls of other gasifiers. Because biomass material is a feed fuel that generally contains high levels of corrosive ash, a fluidized bed gasifier may be often utilized for converting biomass feed material to synthesis gas through the process of gasification.
Typically, the biomass material is fed to the fluidized bed gasifier through a single inlet defined by the fluidized bed gasifier. In feeding the biomass material into the fluidized bed gasifier through the single inlet, the reaction in the gasifier may occur in only a portion of the gasifier causing undesirable pressure and temperature differentials in the gasifier. Such a pressure and temperature differential may result in a portion of the biomass material exiting the gasifier unreacted, thus resulting in lower process efficiency.
What is needed, then, is a system for feeding biomass material into a fluidized bed gasifier such that the homogeneity of pressure and temperature in the reactor is increased, thereby resulting in an improvement in the conversion of biomass material to synthesis gas and increased process efficiency.